Method of treating a body vessel or duct with radiation from within the lumen

ABSTRACT

A method is disclosed to treat the wall of a blood vessel from within the lumen thereof with a radiation catheter that includes a working or radiotherapy lumen, a longitudinally channeled distal balloon, and a balloon inflation lumen. The method includes steps of inserting the catheter into the vessel lumen until the balloon is adjacent a target site of the vessel wall to be treated, inflating the balloon to substantially center the catheter radiotherapy lumen within the vessel lumen at the target site while allowing perfusion of blood past the inflated balloon through channels formed by the balloon, advancing a radioactive source into the catheter radiotherapy lumen to position the source within a region of that lumen along a portion of the catheter occupied by the balloon; and withdrawing the source after it has been positioned within that region of the radiotherapy lumen for a predetermined interval of time.

BACKGROUND OF THE INVENTION

[0001] The present invention relates generally to radioactive sourcesused for treatment of tissue in the human body. More particularly, theinvention resides in a device, apparatus, and methods for treatingtissue by irradiation with a predetermined dose from a radioactivesource which is delivered into the body of the patient via a natural orartificial pathway for a very brief treatment interval or fractionatedtreatment sessions. The device, apparatus and methods of the inventionare especially well suited for brachytherapy in which a malignant tumoris exposed to localized in vivo radiation from a pathway within oradjacent the tumor site, or for controlled irradiation of the wall of ablood vessel, particularly coronary arteries or related blood-carryingcanals, to condition the interior surface thereof against restenosis.

[0002] Brachytherapy, a technique for radiation treatment of malignanttumors, attacks the tumor from within the body. The method typicallyutilizes a radioactive source wire in which a radioisotope sealed at andsubstantially integral with the distal tip of a relatively thin wire orcable is delivered via a pathway formed by a catheter or through anatural cavity, duct or vessel of the body directly to the tumor sitefor localized irradiation. One or more catheters, for example, may beimplanted in the patient's body to provide the pathway(s) from a pointexternal to the body to and through the tumor site, so that the interiorof the tumor mass is accessible via the catheter(s). The radioactivesource, with a dose that may range from about one curie to about tencuries, is mechanically delivered to the site either by hand feeding thesource wire (for low dose and more readily accessible tumor sites) or bymeans of apparatus known as an afterloader which has a drive system towhich the proximal end of the source wire is connected.

[0003] Usually, the treatment is fractionated, in that repeated shortintervals of treatment are performed, with the source wire beingintroduced for the irradiation, left in place for the predeterminedinterval prescribed by the attending oncologist (often afterconsultation with a physicist who has calculated the size of the tumor,the distance to be traveled by the source, the nature of the pathway tobe traversed and likely travel time, and other pertinent factors), andthen withdrawn into the afterloader's shielded safe. To permit treatmentto be performed through multiple catheters to the tumor site, if deemedappropriate by the oncologist, the afterloader may be provided with aturret for automatic delivery of the source wire in succession to theentry points of the several catheters for automated advancement,treatment and withdrawal in each pathway. The desired treatment time ineach case is programmed into the afterloader's control unit.

[0004] The treatment regime may be repeated at regular intervals over aperiod of many days, weeks or months, and, if successful, results incomplete destruction or at considerable shrinkage of the tumor(s). Amongthe advantages of this type of radiation therapy are exposure of thetumor to fractionated treatment doses of localized radiation so thateach individual treatment need only be of extremely short duration toprovide the desired effect while reducing the extent of patient exposureand discomfort, and to provide relatively rapid shrinking of the tumorwhile avoiding prolonged exposure of healthy tissue to radiation.

[0005] Because this type of therapy is more applicable to inoperablemalignancies deep within the body, the site of the tumor(s) is usuallydifficult to reach as the source wire is guided through the pathprovided by the implanted catheter. The catheter itself may bepositioned in place using a previously implanted guidewire or “rail”over which it is advanced along a lumen distinct from the lumen of thecatheter through which the source wire is advanced and retracted. It isoften the case that this pathway is long, extremely narrow and tortuouswith numerous bends and turns. It is essential, therefore, that thesource wire should be suitably thin, strong and flexible to traverse thepathway. Furthermore, the wire must be adapted to carry a suitably sizedradioactive source, i.e., the core which, for high dosage treatments, istypically substantially pure iridium processed in a neutron flux toproduce the radioactive isotope Ir-192. Hence, the source wire has theconflicting requirements that it be of sufficiently small diameter andflexibility to traverse the path to and from the tumor, sufficientlystrong along with its flexibilty to be driven through the pathwaywithout binding or kinking during wire advancement, and with thecapacity to deliver a radiation dosage of as much as ten or more curies.

[0006] Prior art source wires include cable composed of a multiplicityof tiny strands of stainless steel wire to provide both desired strengthand flexibility, but which lack the size or diameter to travel throughthe smallest sizes of pathways required for brachytherapy treatment ofcertain tumors, such as in or through the biliary tract or the bronchiof the lungs. Also, cable source wires typically require welding a plugor capsule containing the radioactive source to the distal tip, whichcreates a point of weakness where fracture may occur. It is imperative,of course, that the source wire be sufficiently sound and reliable toavoid even the remote possibility that it may break and cause theradioactive material portion to be left in the patient's body for aprotracted interval of time.

[0007] Solid source wire is capable of accommodating the Ir-192 or othersource material in a hole formed in the distal tip of the wire toprovide better sealing and security of the source material. Also, solidsource wire can be produced by specialized techniques in sizes rangingdown to from about 0.6 to 0.7 millimeter (mm) diameter to accommodate anIr-192 source having a dosage or radioactive level or strength of up toabout 10 curies. Other conventional source materials include cobalt,cesium, palladium, gold, and iodine. The source wire may be composed ofstainless steel, platinum or certain other conventional materials ofsuitable flexibility.

[0008] For low dose sources in particular, such as one curie or slightlyhigher, the source material may be installed and the entire source wirethen subjected to processing in a nuclear reactor to impart the desiredlevel of radioactivity to the source material. This is an acceptableprocedure where the half-life of the wire material is considerably lessthan that of the source material, so that the radioactivity of the wirematerial itself is sufficiently dissipated to permit it to be usedwithin a few days after activation. Platinum wire, for example, issuitable for that purpose. For higher dose sources, the source materialalone is subjected to the neutron flux and subsequently assembled in thewire by means of shielded, remotely controlled handling and manipulatingtechniques.

[0009] Recently, it has been found that radioactive irradiation of theinterior wall surface of blood vessels in general and the coronaryarteries in particular with a low dose source for a very brief intervalfollowing treatment of the vessel for removal or compression ofoccluding material such as plaque, enjoys marked success in preventingrestenosis. Restenosis is a recurrence of the stricture or narrowing ofthe vascular lumen or heart valve following surgery or other treatmentfor removal or reduction of an occlusion, or from related trauma. Forexample, cardiac patients who have been treated by balloon angioplasty,artery interior wall scraping, laser removal of plaque, by-pass surgery,and other conventional techniques for treating stenosis or occusion ofthe blood vessels either because of or in avoidance of myocardialinfarction, have been found to experience high incidence of restenosis.

[0010] Approximately one-third of the patients who have had arteriesunblocked suffer restenosis about six months later, requiring that theprocedure be redone. And in fact, repeating the procedure appears toincrease the trauma to the smooth muscle cells and to speed theirregrowth. Fifty percent of the patients experience some form ofreocclusion of the treated vessel. While a repeat procedure may not berequired for all of those patients, some reocclusion does occur. Theremaining 50% of the patients seem to suffer no reocclusion, and thereis no single explanation for it.

[0011] The fact that one-third of all patients require retreatment, atsubstantial additional cost and with potential loss of life raisesquestions concerning the significance of a 95% success rate for theinitial unblocking procedure. Moreover, if a second reocclusion occurs,the next procedure performed on the patient is likely to be open heartsurgery.

[0012] Restenosis, then, is really an injury response mechanism to theunblocking procedure, at least for some subtantial percentage of thepatients. Attempts to correct the restenosis problem by use of drugshave not been successful.

[0013] Irradiation of the vessel wall with a radioactive source appearsto alleviate the problem in tests conducted on rabbits and rats, butcreates a new problem in that the source wire must be sufficiently thin,flexible and strong to be capable of placement in the offendingarteries. This is by no means a simple task, because of the small sizeof the vessels, the difficulty in reaching the target area through theartery as a consequence of the small size of the target and the tortuouspathway involved, and especially the susceptibility of the patient to aheart attack if the critical vessel is blocked for an inordinate timeduring performance of the treatment.

[0014] The problems involved are similar to, if not greater than, thoseencountered in treatment of tumors by brachytherapy as described above.It is a principal object of the present invention to provide new andimproved source wires, apparatus and methods for in vivo, localized,internal radioactive treatment of selected tissue in the human body.

[0015] The cost of treatment for heart attack victims is staggering, andis among the procedures being addressed in a strong effort toward costcontainment by treatment centers and other care providers. Of course, iftreatment is unsuccessful, inadequate or untimely, the cost is evengreater—in loss of life. Therefore, it is another important object ofthe present invention to provide improved and lower cost means andmethods for treating cardiac patients to avoid restenosis of the veinsand arteries, and even of the heart valves, following procedures used toopen a blocked or partially blocked or inoperative blood passageway.

SUMMARY OF THE INVENTION

[0016] According to the present invention, a new and improvedradioactive source wire is provided for use both in brachytherapy andcardiac treatment for the purposes described above. In particular, thesource wire is composed of a nickel-titanium alloy known commercially asnitinol which has the desired properties of flexibility, springiness,slipperiness, mechanical strength and super-elasticity, and whichreturns to a straight shape after it is withdrawn from the narrowtortuous pathway through which it was driven for purposes of treatment.The radioactive source material, such as Ir-192 (iridium isotope)spheres, is loaded in an axial hole in the distal tip of the wire, whichis then sealed with a nitinol plug as by welding. The nitinol sourcewire is readily returned to the drive system of the afterloader withoutlikelihood of kinks or bends, for subsequent use in another or otherprocedures of the same type.

[0017] The wire is composed of a shape memory alloy, the nickel/titaniumalloy nitinol being preferred, possessing super-elastic properties andthe capability, at proper temperature, of transforming from anunstressed austenitic state (being a straight configuration) to a stressinduced martensitic state and the capability of returning to theaustenitic state when the externally induced stress is removed. Thedeformations encountered in tortuous pathways are fully recoveredwithout permanent plastic deformation, and the material transforms tothe stable austenitic state for storage or spooling with no permanentdeformation from the prior use.

[0018] Nitinol has been used commercially in bendable frames for lenses(eyeglasses). It has also been used in the past for rails (guidewires)that are employed in various parts of the body by placement through alumen to define a selected site as a means to transport and retrieveitems to and from that site. In this way, the rail dispenses with theneed to relocate the the selected site repeatedly, such as for placementof catheters. However, to our knowledge, there has been no suggestionthat nitinol would serve a useful purpose as a source wire forradioactive source material.

[0019] The procedure for which the nitinol source wire is used may be abrachytherapy application or a coronary radiotherapy application. Thesame basic afterloader drive system is used for both applications,although the machines themselves are somewhat different. For example,the brachytherapy (oncology) afterloader is more complex only because ofthe large variety of targets (tumors at sites possibly anywhere in thebody, versus targets at or in the region of the heart for the coronarymachine), and up to about 20 channels versus only one channel requiredfor the coronary radiotherapy machine. The radioactivity shielded safeis larger on the oncology machine because the source is of greaterradioactivity level. Also, in the coronary machine it is not necessaryto use a turret, or at maximum, a two-position turret, whereas theturret of the brachytherapy afterloader has a number of positionscorresponding to the array of channels available for delivery oftreatment. The basic structure of each machine may be entirelyconventional.

[0020] In the coronary radiotherapy treatment procedure of theinvention, the afterloader equipment is adapted to advance a dummy wire(non-radioactive) through the implanted catheter to the target siteunder visual observation such as fluoroscopy, after which the dummy wireis retracted, and the source wire is then automatically advanced to thetarget site through the catheter for localized irradiation of the vesselwall over a very brief period of time that depends on the radioactivitydosage prescribed by the attending physician. The dummy wire has anopaque tip marker to facilitate the fluoroscopic observation, and theprecise location of the target area along the pathway is calibrated inthe afterloader according to the measured distance of travel by thedummy wire. The treatment is performed automatically by remote operationof the afterloader which is located in a radiation-shielded room wherethe patient is placed for the treatment.

[0021] A treatment catheter is coupled to the end of the afterloaderconnector and deployed over a rail guidewire to the target site forultimate delivery and retraction of the radioactive source. In the caseof coronary radiotherapy, the source material in the source wire must becentered to provide uniform irradiation to achieve maximum results. Anon-centered source could deliver too little radiation to one side ofthe artery interior wall, resulting in no effective treatment of thatregion, and too much to the other side, resulting in possible injury tothat portion.

SUMMARY OF THE DRAWINGS

[0022] The above and still further objects, features and attendantadvantages of the present invention will become apparent fromconsideration of the following detailed description of certain presentlypreferred embodiments and methods of the invention, taken in conjunctionwith the accompanying drawings, in which:

[0023]FIG. 1 is a simplified view of a typical arrangement forimplementing a procedure with a brachytherapy system or a coronaryradiotherapy system according to the present invention;

[0024]FIG. 2 is a fragmentary, perspective view of a catheter, rail, andsource wire connected at the proximal end to the afterloader driveconnector;

[0025]FIG. 3 is a simplified side view of the system of FIG. 2;

[0026]FIG. 3A is a sectional view through the lines A-A of FIG. 3; and

[0027]FIG. 4 is a fragmentary sectional side view of the source wireshowing an exemplary assembly of the radioactive source material andspecial wire material according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT AND METHOD

[0028] Referring to FIG. 1, the invention in one of its aspects is usedin treatment regimens provided by a brachytherapy system or a coronaryradiotherapy system. In practice, the patient 10 is moved into aradiation-shielded treatment room where the procedure will be performed.A treatment catheter 12 is implanted in the patient, and, in thecoronary or cardiac procedure is also coupled to a connector of thedrive system for the remote afterloader 15. The drive system, andindeed, the entire afterloader may be completely conventional for thebrachytherapy application, and would require only a few chnages for thecardiac application.

[0029] It will be understood that while both uses are described in thisspecification, in the typical case, the patient will go through only oneof the two procedures. Also, separate afterloaders and treatment roomswould be provided for the two different applications. The decription ofboth procedures here is solely for the sake of convenience, and becausemany aspects of the present invention are applicable to both types oftreatment.

[0030] For treatment, the patient 10 is placed in a supine or a proneposition on a table 17, with the afterloader 15 placed in closeproximity to allow the source wire of the afterloader to be deployedthrough the treatment catheter into the selected target site in thepatient's body. The afterloader is controlled by the attendingphysician, an oncologist in the case of brachytherapy treatment or acardiologist in the case of cardiac treatment, and/or by aradiotherapist 20 from a control console 22. In practice, the controlconsole may be in the treatment room where low dose radioactivitytreatment is being performed, but shielded with the attendant by a setof radiation screens 25, or may be located outside the shieldedtreatment room for high dose radioactivity treatments.

[0031] A fluoroscope 28 is positioned above the patient, although itsuse would usually be required only for the cardiac treatment. A videocamera and display monitor 30 are positioned to allow attendant 20 toview the patient, with equipment including display controls 31positioned within easy access to the attendant.

[0032] The method used in performing brachytherapy is entirelyconventional, and hence, only portions of it will be described here inthose portions of the text where appropriate. Description of the methodand certain specialized apparatus employed for the cardiac treatmentwill be described presently. First, however, it is desirable to describeaspects and features of the preferred embodiment of a source wire which,except for radioactive dosage requirements, may be used for eitherprocedure.

[0033] According to the preferred embodiment of the invention, thesource wire is an assembly of an elongate wire composed of anickel/titanium alloy commercially marketed as nitinol. Nitinol isavailable, for example, from Shape Memory Alloys of Sunnyvale, Calif.The material is described, for example, in U.S. Pat. No. 4,665,906. Forpurposes of the source wire application according to the invention, thenitinol in the form of a wire is stored in its austenitic state (belowthe transition temperature, discussed below), characterized by astraightened shape, and when used is flexed to put it in astress-induced martensitic state (above the transition temperature),which is characterized by super-elasticity. When the wire is formed, theprocess, which involves several separate treatments at high temperature,produces a transition temperature of the material between its austeniticstate in which it is ductile, to the stress-induced martensitic state.In source wire of the invention, the nitinol is always used fortreatment at a temperature above the transition temperature, which istypically 15° C.±5° C., for example, and is in the austenitic stateexcept when the wire is in flexation at which it is in thestress-induced martensitic state. This is the case for the nitinol wireused in either of these applications, where it is bent and flexed as itmoves through a tortuous path in the human body in the brachytherapytreatment or cardiac treatment procedure.

[0034] The transition temperature may be varied somewhat as a functionof the manner in which the nitinol wire is processed, especially itsheat treatment. For example, in one form in an austenitic state the wirematerial was floppy, which did not adversely affect cycling tensilestrength or shear strength. In the preferred form the nitinol wire has asufficient memory aspect to retain straightness despite a capability tobe

[0035] For purposes of assuring retention of its desired properties inthat state, such as the properties of high flexibility, springiness,slipperiness and mechanical strength, the nitinol wire is heat treatedwhile it is being processed to form wire of the desired diameter for usein the brachytherapy and coronary radiotherapy applications of theinvention. As with stainless steel rods and wires, nitinol can be drawnand successively redrawn to progressively smaller diameters.

[0036] Because the manufacturing process can affect the wire'sproperties, it is important to verify metallurgical specifications aspart of the testing of the wire for performing validations, includingbasic factors such as ultimate tensile strength. Cycling of the wire(i.e., putting it through tests in which it is used and reused in theintended manner for the application) is important to detect otherwiseunseen characteristics that may adversely affect its performance, suchas case hardening due to grinding, and to assure absence of lot-to-lotvariations.

[0037] Three different processes were employed to produce the nitinolwire for use in source wire according to the invention. It was necessaryboth to produce the wire in its final form (i.e., dimensional includingdiameter and length) and to provide it with a cavity in whichradioactive source material would be retained. In particular, an axialhole is formed at the distal end of the wire to house the sourcematerial, which would subsequently be sealed to prevent particulate lossand contamination.

[0038] One process of producing the wire with an axial hole at its tipinvolved drilling a hole in an oversize wire or rod, followed byrepeated drawing of the wire through progressively smaller dies untilthe desired wire diameter and hole depth were achieved. During thedrawing stages the depth of the hole underwent lengthening, as would beexpected, so it is necessary to calculate the desired final depth andfrom that, determine the depth of initial drilling of the hole. Wirediameter of 0.023 inch and hole diameter of 0.014 inch is preferred.This hole drilling and drawing process to provide the final form of thewire and desired properties was performed for the assignee of thepresent application by the Raychem Corporation of Menlo Park, Calif.

[0039] A second process, also performed by Raychem Corporation, produceda similar form of wire which constitutes a thin-walled nitinol tube cladover a nitinol backbone wire running substantially the entire length ofthe tube except for a portion at the tip. This portion provides the holeof desired depth to house the source material. Other dimensions of thetube/backbone wire are substantially the same as those described abovefor the drilled hole/drawdown version of the wire. A slightly greaterouter diameter of 0.022 inch resulted from this process.

[0040] A third process, which was used only to produce the axial hole inthe tip of a nitinol wire of the final desired diameter, involved theuse of electrical discharge machining (EDM) performed by Mega TechnologyEDM, Inc. of Norcross, Ga. In contrast to the other processes, the EDMprocess has tended to produce a hole wall of somewhat varying thickness.In any event, however, the EDM process did produce a hole of desireddiameter and depth in the end of the wire without need for furtherdrawing.

[0041] A fragmentary portion of the final source wire is shown in theside sectional view of FIG. 4. The nitinol elongate wire 38 with axialhole 39 in its distal tip is loaded with radioactive source materialsuch as iridium isotope Ir-192 spheres 40 of slightly smaller diameterthan that of the hole 39. The radioactivity level of the total sourcematerial in the wire is preferably about one to two curies (a low dosewire) for the cardiac application, and from that dose up to about 10curies (a high dose wire), depending on physician-prescribed dosage, forthe brachytherapy application.

[0042] After loading the source material, a nitinol plug 42 ofpreferably rounded shape is inserted into hole 39 to tightly cap it. Theplug is then welded to seal the hole against loss of any sourcematerial. The source material may be enriched Ir-192, and in any eventis substantially pure iridium converted to radioactive form by treatmentin a nuclear reactor in a known manner. The radioactive spheres areassembled in the nitinol wire and the hole is sealed with the weldedplug by manipulations performed using remote manipulators in an assemblyarea.

[0043] A feature of the preferred embodiment of the source wire is thatit may be tapered down at the distal end to provide even greaterflexibility in reduced size at the point of delivery of the dosage tothe target which is to be irradiated. A somewhat larger diameter of thewire up to the point at which the taper begins is useful to provide thecolumn strength sufficient for drivability of the wire by theafterloader. For example, in the embodiment of FIG. 4 the distal end 45of the wire may be tapered over the last six inches to the tip, bydrawing that portion through an appropriately sized die. The taperingprocess would be performed prior to loading radioactive source material.

[0044] If a multi-strand cable were used in place of a solid wire forthe source wire, the cable can similarly be tapered. This isaccomplished by tapering every strand at the distal end, so that whenthe strands are is twisted to produce the final form of the cable, ithas a rat-tail shaped taper. Although it is not the preferred mode of asource wire, the multi-strand cable form may be assembled with a smallcapsule containing the radioactive source material, by welding thecapsule to the distal tip of the cable. Each strand may have anextremely small cross-section, e.g., 0.001 inch, so that it bendseasily, making the overall cable very flexible. Such cables have beenproduced without taper in stainless steel, but a form used in accordancewith the present invention would employ nitinol strands.

[0045] By way of comparison, a nitinol solid wire has almost twice thecolumn strength of a multi-strand stainless steel cable of correspondingdiameter. Multiple strand cable ordinarily has a slight advantage inflexibility, but the nitinol material tends to reduce that advantage byvirtue of its flexibility, even as a solid lead. Such flexibility isespecially important in the applications described herein. Insufficientflexibility can cause the wire to develop small kinks as it travelsthrough curves in the catheter, and the kinks become of greater width inany short section of the wire than the width of the catheter lumen.Consequently, the wire will lock in the catheter, perhaps so much sothat it becomes immovable in either direction. This is completelyunacceptable where a radioactive source wire is being used.

[0046] In the method of the invention, a treatment catheter 12 (FIGS. 1,3) is implanted in the patient to provide the pathway to be traveled bythe source wire, and the wire is advanced (or withdrawn) in that pathwaythrough the catheter during the treatment procedure, whether forbrachytherapy or for coronary radiotherapy. Of course, the selectedtarget is different depending upon application.

[0047] In the cardiac application, the catheter is also coupled to theafterloader connector 50 by a guidewire or rail 52 which extends to thetarget site. The catheter for that application may be provided withsmall channels to allow some blood flow therethrough. The catheter 12 isplaced over the rail 52 which is hooked into the connector for theafterloader as well. The afterloader connector 50 is also coupled to theturret. A key 55 is used to lock the coupling in place and prevent thecatheter and the rail from undergoing rotation.

[0048] Since the rail lumen 58 (FIG. 3A) is at the top of catheter 12,the key 55 on the afterloader coupling 50 locks the catheter againstrotation. If the catheter were allowed to rotate, the rail (guidewire)52 would begin uncontrollable spinning because of the eccentricity ofits lumen 58 in the catheter. Orientation of the guidewire channel isalso extremely important, and is maintained by the key.

[0049] The cardiac application of the radioactive source wire isextremely size sensitive. Among critical issues for that application areflexibility for access through the fine and tortuous pathways to thevery fine and remote blood vessels, and size for entry into the vessels.

[0050] A suitable level of radioactivity (dosage) for the source in thisapplication is one curie, and such a source would be kept in place aperiod sufficient to produce, say, 1,000 to 1,500 rads at one millimeterdistance from the vessel or valve wall. Radioactivity delivered to thewall surface depends on factors such as the length of source, the lengthof the lesion and the curie level on the day the treatment is performed,and the length of time of the treatment.

[0051] The patient can only tolerate one to one and a half minutes oftotal occlusion in the target area, which means that the treatment mustbe stopped before the limit is reached, the attending personnel thenreturn, the balloon is deflated to allow the heart (or the portion beingtreated) to reoxygenate. After an interval of, say, three to fiveminutes, the treatment procedure is recommenced to apply the remainingdosage required to irradiate the target area by redeployment of thesource wire and the centering balloon.

[0052] It is also imperative to provide centering of the wire in thevessel, although somewhat less so with a small diameter artery because,for example, one side may be 2½ mm and the other may be 2 mm. The needto center exists to avoid a hot spot on one side. Preliminary resultsalso indicate that a failure to obtain a certain threshold of radiationon the vessel wall, about 1,000 rads, will result in no discernibleprevention of restenosis.

[0053] In the preferred embodiment, an inflatable balloon is provided inthe catheter for centering the source tip of the source wire. A dose of1,000 to 1,500 rads drops off according to the inverse square of thedistance, so that a distance of 5 mm from the vessel wall to the source(atually the tip of the source wire), causes the field strength to dropoff sharply, with concomitant loss of threshold. The treatment cathetermay include, in addition to the working treatment (radiotherapy)channel, the rail (guidewire) channel, an inflation channel for thecentering balloon. Segmented or scalloped balloons, or otherwisechanneled balloons may be used, together with a channeled catheter oralone, to permit some flow-by of blood sufficient to avoid completeblockage during treatment.

[0054] For treatment at the bottom of the heart, a scalloped catheterwith no balloon is preferred. In that situation, centering of the sourcewithin that treatment area with some blood flow-by capability isachievable without need for a balloon.

[0055] A different type of centering mechanism may be used, and in thatevent could be of a type and shape that would permit sufficient bloodflow so that the procedure need not be stopped before the treatmentregimen is completed. The problem of using a different mechanism isprincipally in the means for deployment. Balloon inflation and deflationin a catheter is in and of itself an entirely conventional technique andhas a proven record of safety.

[0056] The irradiation procedure is preferably performed very soon afterthe balloon angioplasty (PTCA) or other unblocking procedure iscompleted on the vessels. The rail (guidewire) is left in place duringthe period of treatment because it allows a rapid return to the target.Since the rail is tiny, at 0.014 inch, it does not seriously impedeblood flow. Initially, the rail is steered into the part of the heartbeing targeted, using a fluoroscope, becomes the first component in andthe last out.

[0057] If not installed properly, a branching effect can occur. Thus,the catheter and subsequently the source wire must be advanced to thedesired branch via the rail. The catheter is placed over the rail, andin available size ranges, is capable of moving through vessels or ductsas small as two mm in diameter.

[0058] Lumen diameter of the artery dictates the choice of treatmentcatheter as well as the radioactivity dose. If it is determined that thedose should be 1,450 rads, for example, that value is entered on thecontrol console of the afterloader, or other factors may be entered bywhich a microprocessor in the control console may calculate the doseaccording to location of the target, size of lumen, center of the lumen(distance to the interior wall surface), curie rating per day, and otherknown factors.

[0059] A fail-safe function of the afterloader senses patient problemswhen the coronary radiotherapy is administered. In the event that thepatient is experiencing pain or other difficulties, the source wire ispromptly drawn back and the balloon is deflated and the patient's heartis allowed to reoxygenate. The target location is marked with a dummywire deployed from the afterloader. The control console of theafterloader enables programming of the desired functions. A one to oneand one-half minute interval is timed by the afterloader, the procedurehalted at that point, the source wire is retracted into the safe. Theafterloader retains all necessary data such as the dose given and thedose given on transit to and from the point at which initiated, ortransit dose, and treatment is recommenced after a break of two or threeminutes.

[0060] Although a preferred embodiment and method of the presentinvention has been described herein, it will be apparent from theforegoing description to those skilled in the field of the inventionthat variations and modifications of the invention may be implementedwithout departing from the spirit and scope of the invention.Accordingly, it is intended that the invention shall be limited only tothe extent required by the appended claims and the rules and principlesof applicable law.

What is claimed is:
 1. A source wire for treating tissue within apatient's body by localized in vivo radiation of tissue at a target sitefrom a radioactive source of the source wire, the source wire beingintroducible by applicator to the target site via an implanted catheteror a natural vessel, duct or chamber of the patient's body that providesa pathway or portion of a pathway to the target site from a pointexternal to the body, said source wire comprising: an elongate wirecomposed of nickel-titanium alloy, having preselected properties offlexibility, springiness, slipperiness, mechanical strength and shapememory retention, said elongate wire having a proximal end and a distalend, and a radioactive source assembled with said elongate wire at thedistal tip thereof for delivery through said pathway to the target siteby loading and advancing the elongate wire along the pathway from theproximal end of the elongate wire, until the source is disposed at thetarget area for irradiating the selected tissue.
 2. The source wire ofclaim 1, wherein: the elongate wire is a solid lead of substantiallyuniform thickness along its entire length.
 3. The source wire of claim1, wherein: the elongate wire is a cable composed of a multiplicity ofstrands of substantially uniform thickness throughout the entire lengthof each strand, each strand having a distal end and a proximal end. 4.The source wire of claim 3, wherein: the distal end of at least some ofthe strands is set back relative to the distal end of the elongate wireand to the distal end of other strands of the cable, to form a taperthat narrows from a point short of the distal end of the wire to thedistal end of the wire, for ease of entry into portions of the pathwayof reduced size.
 5. The source wire of claim 2, wherein: the elongatewire has an axial hole of predetermined depth at its distal tip, thesource is disposed in said axial hole, and a plug is fastened to thedistal tip of the elongate wire to seal said axial hole with the sourcedisposed therein.
 6. The source wire of claim 5, wherein: the sourcecomprises an iridium isotope that has been irradiated to a predeterminedradioactivity level for treatment of the tissue in the target area. 7.The source wire of claim 6, wherein: the source comprises a plurality ofsegments of said iridium isotope.
 8. The source wire of claim 6,wherein: the iridium isotope has a radioactivity level of at least onecurie.
 9. The source wire of claim 6, wherein the tissue to be treatedis a malignant tumor, and the iridium isotope source has a radioactivitylevel of approximately 10 curies.
 10. The source wire of claim 9,wherein: the elongate wire has a diameter less than approximately 0.028inch.
 11. The source wire of claim 6, wherein the tissue to be treatedis an interior surface of a vascular wall which has been subjected totrauma by prior treatment to reduce the presence of plaque, and theiridium isotope source has a radioactivity level in the range ofapproximately 1 to 2 curies.
 12. The source wire of claim 11, wherein:the elongate wire has a diameter less than approximately 0.021 inch. 13.The source wire of claim 1, wherein: the elongate wire is an assembly ofa tube and a solid backbone wire running the entire length of the tubeexcept for a displacement of the end of the backbone wire relative tothe same end of the tube to form an axial hole of predetermined depth toaccommodate radioactive source material therein, and a plug fastenedover the open end of the axial hole to securely seal the source materialtherein.
 14. A method of treating smooth muscle cell tissue within thebody of a patient, using a radioactive source wire, comprising the stepsof: implanting a catheter in the patient to provide a pathway from apoint external to the patient's body to a point at or near apredetermined target area about the patient's heart for the tissue to betreated, advancing a source wire including an elongate lead having adistal end with a radioactive source thereat and a proximal end fromwhich the source wire is advanced, through the catheter by limiting theelongate lead to a sufficiently small diameter to carry the radioactivesource to the immediate vicinity of the tissue for irradiation thereofin the target area, having selected the elongate lead to be sufficientlyflexible and mechanically strong to traverse the catheter withoutsubstantial kinking while resisting breakage, halting the advance of thesource wire through the catheter when the distal end reaches the pointat which the source wire is to irradiate tissue in the target area,irradiating the targeted tissue for a predetermined interval of time,and withdrawing the source wire from the catheter immediately uponcompleting the irradiation of tissue for the duration of the interval.15. The method of claim 14, wherein the target area is a coronaryartery, and further including: centering the distal tip of the sourcewire in the coronary artery to produce subtantially uniform irradiationof the radioactive tissue adjacent the source,
 16. The method of claim15, further including: performing the irradiation substantiallyimmediately after the coronary artery has been subjected to opening ofthe lumen by reduction of the thickness of plaque on the interiorsurface of the wall of the artery, to produce subtantially uniformirradiation of the radioactive tissue adjacent the source, and therebyreduce the likelihood of restenosis of the irradiated interior surfaceof the artery wall.